The prostate gland, which is found exclusively in male mammals, produces several components of semen and blood and several regulatory peptides. The prostate gland comprises stroma and epithelium cells, the latter group consisting of columnar secretory cells and basal nonsecretory cells. A proliferation of these basal cells as well as stroma cells gives rise to benign prostatic hyperplasia (BPH), which is one common prostate disease. Another common prostate disease is prostatic adenocarcinoma (CaP), which is the most common of the fatal pathophysiological prostate cancers, and involves a malignant transformation of epithelial cells in the peripheral region of the prostate gland. Prostatic adenocarcinoma and benign prostatic hyperplasia are two common prostate diseases, which have a high rate of incidence in the aging human male population. Approximately one out of every four males above the age of 55 suffers from a prostate disease of some form or another. Prostate cancer is the second most common cause of cancer related death in elderly men, with approximately 96,000 cases diagnosed and about 26,000 deaths reported annually in the United States.
Studies of the various substances synthesized and secreted by normal, benign and cancerous prostates carried out in order to gain an understanding of the pathogenesis of the various prostate diseases reveal that certain of these substances may be used as immunohistochemical tumor markers in the diagnosis of prostate disease. The three predominant proteins or polypeptides secreted by a normal prostate gland are: (1) Prostatic Acid Phosphatase (PAP); (2) Prostate Specific Antigen (PSA); and, (3) Prostate Secretory Protein of 94 amino acids (PSP94), which is also known as Prostatic Inhibin Peptide (PIP), Human Seminal Plasma Inhibin (HSPI), or β-microseminoprotein (β-MSP), and which is hereinafter referred to as PSP94.
PSP94 is a simple non-glycosylated cysteine-rich protein, and constitutes one of three predominant proteins found in human seminal fluid along with Prostate Specific Antigen (PSA) and Prostate Acid Phosphatase (PAP). PSP94 has a molecular weight of 10.7 kiloDaltaon (kDa), and the complete amino acid sequence of this protein has already been determined (SEQ ID NO:1). The cDNA and gene for PSP94 have been cloned and characterized (Ulvsback, et al., Biochem. Biophys. Res. Comm., 164:1310, 1989; Green, et al., Biochem. Biophys. Res. Comm., 167:1184, 1990). Immunochemical and in situ hybridization techniques have shown that PSP94 is located predominantly in prostate epithelial cells. It is also present, however, in a variety of other secretory epithelial cells (Weiber, et al., Am. J. Pathol., 137:593, 1990). PSP94 has been shown to be expressed in prostate adenocarcinoma cell line, LNCap (Yang, et al., J. Urol., 160:2240, 1998). As well, an inhibitory effect of exogenous PSP94 on tumor cell growth has been observed both in vivo and in vitro (Garde, et al., Prostate, 22:225, 1993; Lokeshwar, et al., Cancer Res., 53:4855, 1993), suggesting that PSP94 could be a negative regulator for prostate carcinoma growth via interaction with cognate receptors on tumor cells.
Native PSP94 has been shown to have a therapeutic modality in treating hormone refractory prostate cancer (and potentially other prostate indications).
Metabolic and immunohistochemical studies have shown that the prostate is a major source of PSP94. PSP94 is involved in the feedback control of, and acts to suppress secretion of, circulating follicle-stimulating hormone (FSH) both in-vitro and in-vivo in adult male rats. PSP94 acts both at the pituitary as well as at the prostate site since both are provided with receptor sites for PSP94. It has been demonstrated to suppress the biosynthesis and release of FSH from the rat pituitary as well as to possibly affect the synthesis/secretion of an FSH-like peptide by the prostate. These findings suggest that the effects of PSP-94 on tumor growth in vivo, could be attributed to the reduction in serum FSH levels.
Both PSA and PAP have been studied as tumor markers in the detection of prostate disease, but since both exhibit elevated levels in prostates having benign prostatic hyperplasia (BPH), neither marker is specific and therefore they are of limited utility.
Recently, it has been shown that PSP94 concentrations in serum of patients with BPH or CaP are significantly higher than normal. The highest serum concentration of PSP94 observed in normal men is approximately 40 ng/ml, while in men with either BPH or CaP, serum concentrations of PSP94 have been observed in the range from 300–400 ng/ml. Because there exists some overlap in the concentrations of PSP94 in subjects having normal prostates and patients exhibiting either BPH or CaP, serum levels in and of themselves are of little value.
A major therapy in the treatment of prostate cancer is androgen-ablation. While most patients respond initially to this treatment, its effectiveness decreases over time, possibly because of the presence of a heterogenous population of androgen-dependant and androgen-independent cells to the androgen treatment, while any androgen insensitive cells present would continue to proliferate unabated.
Other forms of cancer, which are currently exacting a heavy toll on population are breast cancer in women and cancer of the gastrointestinal tract. Currently, the use of various cancer drugs such as mitomycin, idarubicin, cisplatin, 5-fluoro-uracil, methotrexate, adriamycin and daunomycin form part of the therapy for treating such cancers. One drawback to such a therapeutic treatment is the presence of adverse side effects due to the drugs in the concentration ranges required for effective treatment.
Accordingly, it would be advantageous to find a more effective means of arresting the growth of prostate, breast and gastrointestinal cancer cells and tumors, which may be used effectively against both androgen sensitive and androgen insensitive cells.
In previous work, described in U.S. Pat. No. 5,428,011, we provided pharmaceutical preparations (i.e., compositions) of native human seminal plasma PSP94 for inhibiting in-vitro and in-vivo cancerous prostate, gastrointestinal and breast tumors. The pharmaceutical preparations included native human seminal plasma PSP94 which could be administered in an appropriate dosage form, dosage quantity and dosage regimen to a patient suffering from prostate cancer. In another embodiment, the pharmaceutical preparation included a mixture of human seminal plasma PSP94 and an anticancer drug which may be administered in an appropriate dosage form, dosage quantity and dosage regimen to a patient suffering from, for example gastrointestinal cancer.
PSP94 sourced from human seminal fluid carries with it significant risk of contamination with infectious agents (e.g., HIV, hepatitis (a, b, or c), and other viruses and/or prions). Even with the use of harsh chemical treatment, total eradication of such agents cannot be guaranteed. Additionally, human seminal fluid is found in limited supply, thus making bulk production of PSP94 very difficult. Therefore, the acceptability of human or even xenogeneic sourced PSP94 may be very difficult for both the regulatory authorities and the marketplace.
Therefore, the use of recombinant technology for producing PSP94 would represent a significant advancement, as recombinant PSP94 could be produced both free of pathogens and in an unlimited supply. Furthermore, the material would be homogeneous from a single lot source, avoiding batch variation.